Transport Airplane Directorate 

1601 Lind Ave, SW. 

Renton, Washington 98057-3356 

March 24, 2011 

Mr. Anthony Beck 

Gulfstream 

P.O. Box 2206 

Savannah, GA 31402-2206 

Dear Mr. Beck: 

We have reviewed your petition for exemption (Docket No. FAA-2010-1119) and 

determined that we require more information before we can continue processing your 

petition. In that letter, you requested partial exemption from the requirements of 

§ 25.981(a)(3) of Title 14 of Code of Federal Regulations (14 CFR) for the Gulfstream 

Model GVI airplane that is currently being evaluated for FAA type certification. The 

exemption, if granted, would permit relief from the requirements of fuel tank structural 

lightning protection. In support of your petition, you submitted a report titled “Structural 

Assessment for Fuel Systems Lightning Protection Certification for FAA 14 CFR 25.981,” 

Document No. GVI-GER-0127. Review of the supporting report indicates additional 

information is needed for our office to process your request for exemption. 

The fault tree analysis provided in your report does not identify any single failures that could 

result in ignition sources being present in the fuel tanks. During review of industry data, 

several failure modes have been identified that can defeat fault tolerant designs. Examples 

include structural cracking, as well as fastener failures that can cause loss of sealant, which 

is the secondary ignition prevention feature. The GVI fuel tank construction and materials 

are similar to those used in other designs where non-fault tolerant features have been 

identified. Therefore, the petition for exemption or report should either be revised to 

identify these features, or Gulfstream should submit data substantiating that these failures 

are not possible on the Model GVI airplane. 

Your petition states that, after considering FAA Policy Memo ANM-112-08-002 and 

reviewing the Model GVI design, Gulfstream has determined that compliance with 

§ 25.981(a)(3) for certain structural lightning is impractical. FAA Policy Memo 

ANM-112-08-002, however, requires petitioners seeking an exemption under this policy to 

substantiate the practicality of eliminating any non-fault tolerant design features. While you 

did not identify any non-fault tolerant features, if any are identified as noted above, please 

provide detailed information and analyses of the practicality assessment that you conducted 

to address the criteria as follows: 

“. . . The petitioner should show that all practical measures have been taken to meet the 

requirements of § 25.981(a)(3) for the fuel tank structure. For the design features for 

which an exemption is sought, the petitioner should show what potentially compliant 

design changes were examined, and what design changes were ruled out based on 

impracticality.” 
2

In addition, please submit detailed information and analyses, as follows, to support your 

request for an exemption: 

1. The analysis should show that the design, manufacturing processes, and 

airworthiness limitations section of the instructions for continued airworthiness 

include all practical measures to prevent, and detect and correct, failures of 

structural lightning protection features because of manufacturing variability, aging, 

wear, corrosion, and likely damage. 

2. The report addresses the basic fasteners used in the wing structure and briefly 

addresses the fuel access doors. However, the report does not address other 

detailed structural design features that could also require specific lightning 

protection. For example, those features could include fuel vents, fuel filler caps, 

pump housings, wing-to-body structural attachments, and flap/slat/aileron hinge 

fittings that could have fasteners that extend into the fuel tank structural supports 

and brackets for fuel and hydraulic tubes. 

3. The report does not describe Gulfstream’s testing plans in order to demonstrate that 

the design provides redundant and effective lightning protection. 

4. The assumed failure rate for fasteners in the analysis is in the range of 10-9. 

Industry experience shows fastener failures do occur; therefore, this rate appears to 

be overly optimistic. Additional substantiation for the assumption should be 

submitted. 

5. The discussion in section 5.6.1 states that: “Sealing and corrosion protection 

aspects of the assembly process ensures no aging effects due to corrosion which 

could jeopardize fastener bonding.” If this statement is intended to indicate that 

the analysis is based upon no corrosion for the life of the GVI airplane, additional 

substantiation for this assumption should be submitted. 

6. The analysis indicates quality assurance is dependent upon detecting fuel leakage. 

Additional information should be submitted on any limitation for dispatch of the 

airplane with fuel leakage present. 

With regard to item 1, your petition discussed manufacturing controls for robotically 

installed fasteners but it did not specifically address inspection of any non-fault tolerant 

design features. We request confirmation that any non-fault tolerant design features will 

receive 100% post-assembly inspection to validate that the features are present at the time of 

manufacture. Further, you identified an inspection interval in the analysis document; we 

also request confirmation that these periodic inspections of all ignition prevention features, 

as well as non-fault tolerant features will be identified as critical design configuration 

control limitations (CDCCLs). 
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If you would like us to further process your petition, please send the information described 

above within 30 days. If we do not hear from you within 30 days, we will close the docket 

without notifying you any further. If you have any questions or require additional time, 

please contact Mike Dostert, (425) 227-2132, mike.dostert@faa.gov

/s/ 

Victor Wicklund 

Manager, Propulsion & Mechanical Systems, ANM-112 

Transport Standards Staff 

Transport Airplane Directorate 

Aircraft Certification Service